There are imaging apparatuses for biometric authentication that, for example, capture an image of palm veins without any physical contact with the palm, and read the palm vein image. Such an imaging apparatus is able to capture an image properly when the object is placed in a predetermined distance range from the imaging camera of the imaging apparatus. Therefore, the imaging apparatus needs to detect the distance to the object.
Thus, there has been disclosed a method for detecting the distance or the like from an imaging camera to an object. This method captures an image of an object with a spotlight projected thereon, and detects the distance from the imaging camera to the object on the basis of the spotlight in the captured image, for example (see, for example, Japanese Laid-open Patent Publication No. 2007-10346).
However, with this method of detecting the distance from an imaging apparatus to an object, in the case where the object is placed close to the imaging apparatus, spotlight projected on the object falls out of the imaging area of the imaging camera, so that the spotlight does not appear in the captured image. When the spotlight does not appear in the captured image, it is not possible to detect the distance from the imaging apparatus to the object. Thus, it is not possible to determine whether the object is close to the imaging apparatus or the object is not present.